This application is based on Japanese Patent Application Nos. Hei. 10-153233 filed on Jun. 2, 1998, Hei. 10-247537 filed on Sep. 1, 1998, and Hei. 10-317983 filed on Nov. 9, 1998, the contents of which are incorporated herein by reference.
1. Field of the Present Invention
The present invention relates to a liquid crystal cell to be suitably adopted in a liquid crystal display device or the like, and a process for manufacturing the liquid crystal cell.
2. Description of the Related Art
In recent years, the liquid crystal cell is utilized as a display element for a TV set, a personal computer or a work station, or a display element for a watch, a calculator or a measurement device because it is suited for a light weight and for a thin shape.
This display element is caused to transmit, reflect or shade a light mainly by utilizing the shuttering action of the liquid crystal.
The liquid crystal to be used in the display element is represented by a nematic liquid crystal or a smectic liquid crystal.
A conventional liquid crystal cell has a cell structure, as shown in FIG. 22. This liquid crystal cell is constructed by interposing a seal 903 in a band shape between the outer peripheral portions of two parallel electrode substrates 901 and 902, by providing a number of spherical spacers 904 between the two electrode substrates 901 and 902 on the inner peripheral sides of the seal 903, and by filling a liquid crystal through a liquid crystal filling port of the seal 903.
Here, the electrode substrate 901 is constructed by laminating a plurality of transparent electrodes 901b, a (not-shown) insulating film and an orientation film 901c on the inner surface of a glass substrate 901a. On the other hand, the electrode substrate 902 is constructed by laminating a plurality of transparent electrodes 902b, a (not-shown) insulating film and an orientation film 902c on the inner surface of a glass substrate 902a. Here, the plurality of transparent electrodes 902b are arranged to intersect the plurality of transparent electrodes 901b. Reference numeral 905 designates a polarizing sheet in FIG. 22.
When the liquid crystal cell is made of a nematic liquid crystal, if caused to establish a flow in the nematic liquid crystal by a local pressure or impact from the outside, its orientation state is restored after releasing the pressure or impact.
When the liquid crystal cell is made of a smectic liquid crystal, however, if an orientation defect in the smectic liquid crystal or a disturbance in the liquid crystal layer structure is caused by a local pressure or impact from the outside, its orientation state is not restored even after releasing the local pressure or impact.
On the other hand, when the liquid crystal cell is made of a smectic liquid crystal, an orientation disturbance or a defect is likely to occur in the smectic liquid crystal at the periphery of the spherical spacer, and the display characteristics of the liquid crystal cell are deteriorated.
For this, it is conceivable (as disclosed in Japanese Patent Application Laid-Open No. 7-318912 or U.S. Pat. No. 5,559,621) that the liquid crystal cell using the smectic liquid crystal is given a cell structure, as shown in FIG. 23.
This liquid crystal cell is constructed by interposing a seal 908 in a band shape between two electrode substrates 906 and 907 parallel to each other, providing a plurality of barrier walls 909 between the two electrode substrates 906 and 907 on the inner peripheral side of the seal 908 and filling a smectic liquid crystal through a liquid crystal filling port of the seal 908.
Here, the electrode substrate 906 is constructed by laminating a plurality of transparent electrodes 906b, an insulating film 906c and an orientation film 906d on the inner surface of a glass substrate 906a. On the other hand, the electrode substrate 907 is constructed by laminating a plurality of transparent electrodes 907b, a (not-shown) insulating film and an orientation film 907c on the inner surface of a glass substrate 907a. 
Each barrier wall 909 is clamped between the orientation film 906d of the electrode substrate 906 and the glass substrate 907a of the electrode substrate 907 so that it is positioned to lie between the adjoining two of the plurality of orientation films 907c. 
According to this liquid crystal cell, each barrier wall 909 exhibits a rigidity enough to prevent a defect in the liquid crystal layer of the smectic liquid crystal even a local pressure or impact is applied to the liquid crystal cell from the outside. In the presence of a linear space between the individual barrier walls 909, it is possible to suppress the disturbance in the orientation of the smectic liquid crystal.
However, in the liquid crystal cell of FIG. 23, at a cooling step of cooling the liquid crystal cell after the two electrode substrates 906 and 907 are filled with the smectic liquid crystal, a zigzag orientation defect A, as shown in FIGS. 24, 25, appears in the liquid crystal layer of the smectic liquid crystal.
This point will be described in detail. When the smectic liquid crystal is used as the liquid crystal, it is necessary to fill the smectic liquid crystal under the circumstance of a temperature (at 80 to 120xc2x0 C.) corresponding to an isotropic phase. After this filling operation, the liquid crystal filling port of the liquid crystal cell is plugged, and the liquid crystal cell is cooled.
In FIG. 26, a xe2x80x9cgraph axe2x80x9d plots changes in a volume change rate against a temperature of the cell structure of a liquid crystal cell when the change at 80xc2x0 C. is xe2x80x9c1xe2x80x9d, and a xe2x80x9cgraph bxe2x80x9d plots changes in the volume change rate against a temperature of the smectic liquid crystal.
It is found from these two xe2x80x9cgraph axe2x80x9d and xe2x80x9cgraph bxe2x80x9d that the coefficient of thermal expansion of the smectic liquid crystal is considerably larger than that of the cell structure. Therefore, after the cooling operation, the smectic liquid crystal shrinks more than the cell structure. This means that the volume shrinkage rate of the smectic liquid crystal is considerably larger than that of the cell structure.
Accordingly, the smectic liquid crystal is pulled by the inner surface of the electrode substrate under its surface tension so that this tension generates a stress in the smectic liquid crystal. As a result, an orientation defect A, as shown in FIGS. 24 and 25, is generated in the liquid crystal layer of the smectic liquid crystal.
If the space between the adjoining two barrier walls 909 is enlarged in the liquid crystal cell of FIG. 23, it is possible to prevent the occurrence of the orientation defect A of the liquid crystal layer, which might otherwise be caused by the difference between the volume shrinkage of the smectic liquid crystal and the volume shrinkage of the cell structure.
However, if the space of the individual barrier walls 909 is taken widely by every two or three of the plurality of transparent electrodes 907b, the dielectric constants between the two electrode substrates 906 and 907 are different from each other at the portions with and without the barrier walls 909 of the two electrode substrates 906 and 907.
As a result, a phenomenon to invite deterioration in the display characteristics such as the crosstalk occurs at the time of driving the liquid crystal cell. That is, in order to prevent this phenomenon, the space of the individual barrier walls 909 has to be so narrowed that the barrier walls 909 are provided for every transparent electrode 907b. 
Other problems on the liquid crystal cell, as shown in FIG. 23, will be described with reference to FIGS. 27 to 29. Here, FIG. 27 is a top plan view of FIG. 23, and FIG. 28 is a section taken along line XXVIIIxe2x80x94XXVIII of FIG. 27. In FIG. 28, there are omitted the transparent electrodes 906b and 907b, the insulating film 906c and the orientation films 906d and 907c. 
In the liquid crystal cell shown in FIG. 23, the phase structure of the smectic liquid crystal makes a complicated phase transition from the liquid phase (i.e., the isotropic phase) in a high temperature state to, for example, a smectic A phasexe2x86x92a chiral smectic C phasexe2x86x92a chiral smectic CA phase, as the temperature lowers.
According to this transition in the phase structure of the smectic liquid crystal, this smectic liquid crystal shrinks in its volume, as shown in FIGS. 27 and 28, to generate a defect that bubbles 910 are produced in the liquid crystal cell.
That is, when a volume of the smectic liquid crystal shrinks, the liquid crystal cell of a structure having the plurality of barrier walls 909 interposed between the two electrode substrates 906 and 907 is disabled to change the space between the two electrode substrates 906 and 907 by the plurality of barrier walls 909.
As a result, a filling portion 911 filled with the smectic liquid crystal in the liquid crystal cell is evacuated to be negative pressure to gasify the gaseous component left in the liquid crystal cell so that the bubbles 910 are produced.
This difficulty is prominent especially when the liquid crystal cell having been filled with the smectic liquid crystal is left in a low temperature state (e.g., xe2x88x9220xc2x0 C.).
This bubbling phenomenon will be described in more detail. The smectic liquid crystal has a high viscosity at the room temperature so that it cannot be injected as it is into the liquid crystal cell.
Therefore, the liquid crystal cell is heated to change the phase structure of the smectic liquid crystal into a liquid phase before the liquid crystal cell is filled with the smectic liquid crystal.
After filling operation, the smectic liquid crystal is slowly cooled to the room temperature so that its orientation may be improved. However, according to this slow cooling, the volume of the smectic liquid crystal shrinks, as indicated by a xe2x80x9cgraph Lxe2x80x9d of FIG. 29. Therefore, even when the smectic liquid crystal reaches the room temperature, it is thought that the inside of the liquid crystal cell is evacuated to be negative pressure as a result of the volume shrinkage of the smectic liquid crystal.
It would be better if the vacuum could be damped by deforming the liquid crystal cell with it, but the electrode substrates 906 and 907 are hard to deform in the presence of the plurality of barrier walls 909. This makes it impossible to damp the vacuum in the liquid crystal cell so that the bubbles are produced in the liquid crystal cell.
The situations in which the bubbles 910 are produced will be described in more detail. These bubbles 910 are linearly produced, as shown in FIGS. 27 and 28, at the individual widthwise centers of the plurality of filling portions 911 formed between the two electrode substrates 906 and 907 by the plurality of barrier walls 909, and in the longitudinal direction of the individual filling portions.
That is, it is thought that the linear bubbles 910 are produced at the widthwise centers of the individual filling portions 911 because the inside of the liquid crystal cell is evacuated by the volume shrinkage of the smectic liquid crystal in the individual filling portions 911 and because the excellent wettability between the smectic liquid crystal and the individual barrier walls made of a proper material establishes a force to attract the smectic liquid crystal toward the individual barrier walls.
Thus, in the display area of the liquid crystal cell, a linear display occurs due to each of the linear bubbles 910.
As a countermeasure against the aforementioned bubble production, it is conceivable to enhance the filling density of the liquid crystal cell with the smectic liquid crystal. This concept is exemplified by a method of filling the liquid crystal cell with the smectic liquid crystal by a pressure, as disclosed in Japanese Patent Laid-Open No. 6-67136 or U.S. Pat. No. 5,576,865. However, this disclosure has been insufficient for preventing the bubble production.
This point will be described in detail. The bubbles or the unfilled regions of the smectic liquid crystal are surely reduced at the room temperature, but the liquid crystal cell may be used at 0xc2x0 C. or lower. Therefore, if the liquid crystal cell is exposed to this low temperature circumstance, the volume of the smectic liquid crystal further shrinks, as indicated by the graph L in FIG. 29, so that the inside of the liquid crystal cell is evacuated to be negative pressure. This evacuation is thought to produce the linear bubbles in the liquid crystal cell. Moreover, the bubbles thus once produced do not disappear but remain even if the temperature of the liquid crystal cell is returned to the room temperature, to cause the display defect in the display area (i.e., the area enclosed by single-dotted lines in FIG. 27) of the liquid crystal cell.
To solve the problems thus far described, the present invention has a first object to provide a liquid crystal cell in which a stress generated in a liquid crystal cell can be reduced.
The present invention has a second object to provide a liquid crystal cell in which a vacuum to be established between two electrode substrates as a result of the volume shrinkage of a liquid crystal having a high viscosity at the room temperature can be damped by communicating between two of a plurality of filling portions formed between two electrode substrates by a plurality of barrier walls through the intervening barrier walls.
Moreover, the present invention has a third object to provide a liquid crystal cell, in which the individual barrier walls are given a proper flexibility for reducing the stress generated in the liquid crystal due to the difference in the volume shrinkage between the liquid crystal and the two electrode substrates in accordance with the cooling after the filling of the space between the two electrode substrates with the liquid crystal by devising the structure of the plurality of barrier walls between the two electrode substrates, and a process for manufacturing the liquid crystal cell.
To achieve the objects, the present invention comprises: two electrode substrates; a band seal interposed between the two electrode substrates at the peripheral edges of the same; a plurality of barrier walls clamped on the inner peripheral side of the seal and between the two electrode substrates at a space from each other and in parallel with each other for forming a plurality of filling portions; and a liquid crystal filling the filling portions between the two electrode substrates through the seal.
Moreover, the pluralities of barrier walls have through holes formed to communicate between the adjoining individual two of the filling portions.
When the individual filling portions between the two electrode substrates of the liquid crystal cell thus constructed are to be filled under a vacuum with a liquid crystal in a soft state, the space between the two electrode substrates is kept unvaried by the individual barrier walls so that the two electrode substrates cannot be deformed to establish vacuums in the individual filling portions even if the liquid crystal is caused to shrink in its volume by the temperature.
Since the individual through holes are formed in the individual barrier walls, the liquid crystal portion in the two filling portions adjoining each other through the barrier walls flows to meet each other through the individual through holes of the barrier walls thereby to damp the vacuums in the individual filling portions.
When the liquid crystal in the individual filling portions shrinks in its volume, the volume of the bubbles in the vicinity of the inner surface of the seal increases with the vacuums because the space between the two electrode substrates is kept invariable by the individual barrier walls. That is, the space between the two electrode substrates cannot be varied so that the volume of the bubbles in the vicinity of the inner surface of the seal increases by the volume shrinkage of the liquid crystal to act in the direction to damp the vacuums.
As a result, the vacuums in the individual filling portions are damped so satisfactory that the linear bubbles in the display area of the liquid crystal cell can be prevented in advance from being produced.
In order to achieve the above-specified objects, another aspect of the present invention comprises: two electrode substrates; a band seal interposed between the two electrode substrates at the peripheral edges of the same; a plurality of barrier walls clamped on the inner peripheral side of the seal and between the two electrode substrates in parallel with each other; and a liquid crystal filling between the two electrode substrates via said seal.
In this liquid crystal cell, each of the plurality of barrier walls has a lower rigidity in at least its portion than that of its other portion.
A portion with a lower rigidity in each barrier wall is thus deformed even if the liquid crystal cell is caused to shrink in its volume by the temperature change. Then, the space between the two electrode substrates accordingly narrows while satisfactorily suppressing the appearance of the stress, which might otherwise be caused by the volume shrinkage.
As a result, even if the liquid crystal shrinks in its volume, no orientation defect occurs in the liquid crystal, but the display of the liquid crystal cell can be retained satisfactory.
According to the present invention, at a barrier wall forming step, a plurality of barrier walls are individually formed in a laminar shape of a resist material as first and second barrier wall portions having different rigidities in their height direction on the inner surface of the one or other electrode substrate.
As a result, at a subsequent cooling step, even if the liquid crystal is cooled to shrink in its volume, the less rigid one of the first and second barrier walls is accordingly deformed. This makes it possible to suppress the establishment of the stress, which is likely to appear in the liquid crystal in accordance with the volume shrinkage and to prevent the orientation defect of the liquid crystal.
In a liquid crystal cell according to another aspect of the present invention, the plurality of barrier walls interposed between the two electrode substrates in parallel with each other include: individual support barrier walls for supporting the space between the two electrode substrates; and at least one seated barrier wall seated on the inner surface of the other of the electrode substrate at a space between the support barrier walls from the inner surface of one of the two electrode substrates.
As a result, the space between the two electrode substrates is so enlarged at the portion of one electrode substrate between the individual support barrier walls as to facilitate the elastic deformation of the portion between the individual support barrier walls.
Even the liquid crystal filling up the liquid crystal cell causes a volume shrinkage due to the temperature change, therefore, the space between the two electrode substrates accordingly narrows while satisfactorily suppressing the appearance of the stress, as might otherwise be caused by the volume shrinkage.
As a result, even if the liquid crystal shrinks in its volume, no orientation defect occurs in the liquid crystal, but the display of the liquid crystal cell can be retained satisfactory.